As of February 18, all cruise ships departing from U.S. ports must send a passenger manifest to the department of Customs and Border Protection no less than 60 minutes prior to departure, which means that all passengers must be checked in and onboard prior to that time.
Some cruise lines have taken a proactive role and are implementing the procedure now. Most lines -- Royal Caribbean, Celebrity, Regent, Crystal, Oceania, Princess -- have implemented a policy that states you must be processed and onboard at least 90 minutes before sailaway or you can be denied boarding.
Norwegian Cruise Line is formulating its official policy at this time and we will provide an update as soon as we know more; a message to travel agents asked that they advise their clients to be at the pier no less than two hours prior to departure. The message also indicated that if an individual attempted to check in within the 60-minute window, that individual would be denied boarding, but if a planeload of passengers was delayed, causing a late arrival at the port, the captain has the discretion to wait for them and delay departure of the ship.
Almost all of the lines currently require electronic document processing prior to arrival at the port, some within 30 days and some as close as 3 days out from departure. Guests are required to transmit passport and other identification details to speed port check-in and for vetting by authorities. These new customs procedures monitor those who have actually boarded the ship on the day of departure.